1. Technical Field of the Invention
The present invention relates to a reusable, resettable indicator that will show when thawing has occurred. The device may be stored at any ambient temperature and simply activated.
The same concept may be used for cooking of many food products such as meat, fish, poultry, and other foods. It can be used for heating foods in microwave ovens. It can also be used to indicate fever.
It has many other uses, such as shipping perishable products to show temperature abuse, frozen blood, pharmaceuticals, fruits and vegetables. It may also be used to show sterilization has been achieved in an autoclave and other applications. It may be incorporated in cooking utensils to provide audible alarms to show when food is cooked.
2. Description of the Prior Art
A provisional patent U.S. Application Ser. No. 60/624383 entitled Critical Temperature Indicator was filed Nov. 2, 2004. Volk Industries has developed and marketed pop up food grade indicators as described in U.S. Pat. Nos. 5,799,606, 5,988,102, etc. This concept uses a solid material to hold a spring loaded element in place until, upon achieving a critical temperature, melts and releases the spring element to visually show an internal critical temperature has been achieved.
This concept has many disadvantages. It is complex and costly; it uses metal components which would not work in a microwave oven. But the bigger problems are virtually all materials are viscoelastic when the melt temperature is approached. Hence the spring may release at a range of temperatures depending on heating rate.
In addition, a sliding mechanical component may allow potential contaminating materials to interact with the food.
Further, it cannot show a lower temperature or warning time before a critical temperature has been achieved.
In an attempt to address some of these flaws, U.S. Pat. No. 6,176,197, entitled TEMPERATURE INDICATOR EMPLOYING COLOR CHANGE by Gary M. Thompson was disclosed. Here, two different melt temperature materials are enclosed in a tubular translucent structure. Upon melting, because of density differences, one material rises and mixes with the other material causing a color change.
While this concept improves on the flaws of previous concepts, it still has some problems. It is not reusable, it does not provide a precursor warning indicator and it also tends to be more expensive and complex, because it is not cold assembled and uses hot fluid materials, it can only be used for high temperature cooking applications.